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Home / Issues / № 3, 2017

Engineering

DEPENDENCE OF THE STABILITY OF THE PRESS-FORMS AND SHELL FORMS ON THE CONDITIONS OF HEAT EXCHANGE DURING CASTING OF VARIOUS MATERIALS
Shaparev A.V., Savin I.A.
Abstract: A lot of attention is paid to the regulation of the temperature regime for casting various materials with diverse temperature factors of the process both in domestic and foreign industry. At present, automatic, semi-automatic and manual devices are used to regulate the temperature regime of casting. With automatic control, the preheating temperature of the molds and the temperature of the liquid metal are maintained within the predetermined limits. In the article the peculiarities of the influence of heat exchange conditions on the resistance of molds and shell molds during casting of metals are considered.

Keywords: mold, die casting, heat exchange, temperature regime.

The temperature regime of the casting includes: the temperature of heating and cooling of the molds before and during operation, the temperature of the liquid metal entering the working cavity, as well as the contact temperature and temperature difference that occur during each casting cycle. [1] For automatic regulation, the most suitable devices are liquid-coolers, which can be used not only organic and inorganic liquids, but also low-melting metallic materials. With semi-automatic control, the temperature of the heating or cooling of the molds is regulated. The use of semi-automatic devices leads to overheating or supercooling of molds and to the formation of unstable contact temperatures and temperature differences, and, consequently, unstable casting quality.

 To heat the molds, in this case, often the liquid metal of the first moldings is used, which can lead to the failure of the molds during the first pressing because of the formation of cracks. Reducing the temperature of the metal being poured to the crystallization temperature of the metal always contributes to an increase in the durability of the molds, since the temperature of the contact and the temperature drop are thereby reduced. For example, when casting zinc alloys in mold inserts made of 4Х5МФС steel, melted in vacuum furnaces, the durability rises from 150,000 to 270,000 cycles. [1] On the one hand, the increase in the heating temperature causes an increase in contact temperature and a decrease in strength properties, which contributes to a decrease in resistance, and on the other hand, its increase leads to a decrease in the temperature drop, temperature stresses and deformations, and, consequently, to an increase in resistance (heat resistance). It has been determined from the experiments carried out that with increasing temperature of mold heating up to 315 ° C, resistance increases and then decreases. The optimal temperature for preheating molds for 4Х5МФС steel and working conditions is within 315 ° C. The data obtained are justified for a flat wall that heats up to lower temperatures. In acute angles, there was longitudinal and transverse deformation. [2] Thus, calculations and experiments show that the preheating temperature of the molds is a very effective measure that increases the resistance of molds, so this reserve should be used in every enterprise.

The most important technological measure that increases the resistance of molds is the timely removal of residual stresses. Of great importance is the interval between vacations, which was chosen in such a way that no cracks or mesh of height would appear before it, but the gap was greatest, which was done on the basis of well-known theories on the account of the resistance of molds. In recent years, in domestic and foreign industry it is considered expedient to use intermediate leave as an activity to increase the durability of molds. These measures make it possible to increase the durability of molds by 75-150%. [3]

The main technological parameters of the process include: temperature conditions, coatings and lubrication, the pressing speed, the inlet and flow of liquid metal in the working cavity, the specific pressures in the pressing chamber and the walls of the molds, the holding time of the castings in the mold at the contact temperature, etc. With increasing speeds of pressing and admission, as well as specific pressure, the durability of molds and rods decreases and the stronger they are. The use of slotted gates with high inlet velocities leads to local wear at the points where the jet of liquid metal strikes the obstacle. [3] Therefore, runner system designs have a significant effect on erosion wear. Smooth quiet filling of the working cavity of molds with minimum speeds and specific pressures is preferable. As the specific pressure increases, the heat resistance, mold resistance, wear resistance and durability of molds decrease. Form stability is reduced due to the fact that as the specific pressure increases, the rate of increase in the flare increases. [4] As the pressure increases, the wear of the jet of liquid metal on the work surface increases. With the increase in the holding time, the resistance of the mold is reduced.

Particular attention should be given to the use of lubricants to increase the durability of molds. Lubricants can be an effective means of prolonging the durability of molds, but greases that meet all the requirements for them are poorly developed. The choice of lubricants is an extremely complex task that requires various solutions of chemists together with foundry workers to solve it. [5]

Thus, the well-founded application of various methods for regulating the thermal state of molds and shell molds for casting various alloys makes it possible to increase both the durability of these forms and the quality of the resulting blanks, while reducing the cost of producing and operating the rigging.



References:
1. Gavariev, R.V., Savin, I.A., Leushin, I.O. Impact of the functional coating on service durability of injection molds for the zinc alloys pressure casting. (2016) Tsvetnye Metally No. 1. pp. 66-70 DOI: 10.17580/tsm.2016.01.11

2. Гавариев Р.В., Савин И.А., Леушин И.О. Оптимизация теплового баланса пресс-форм при литье под давлением Zn-сплавов под давлением Zn-сплавов //"Литейное производство" М.2014 № 7. с.26-29

3. Савин И.А., Леушин И.О., Ульянов В.А., Леушина Л.И. Теоретическая оценка трещиностойкости оболочковых форм точного литья, изготовленных с применением технологии низкотемпературного прокаливания//Справочник. Инженерный журнал с приложением. М.2015. № 9 (222). с. 3-5.

4. Савин И.А., Гавариев Р.В. Особенности проектирования технологической оснастки для получения отливок сплавов цветных металлов//Вестник Казанского государственного технического университета им. А.Н. Туполева. 2012. № 4-2. С. 41-43

5.. Shaparev, A., Savin, I. Calculation of the Amount of the Reduction Required for the Formation of Compound Layers during Cold Rolling of Bimetals. (2016) Materials Science Forum, Vol. 870, pp. 328-333 DOI: 10.4028/www.scientific.net/MSF.870.328



Bibliographic reference

Shaparev A.V., Savin I.A. DEPENDENCE OF THE STABILITY OF THE PRESS-FORMS AND SHELL FORMS ON THE CONDITIONS OF HEAT EXCHANGE DURING CASTING OF VARIOUS MATERIALS. International Journal Of Applied And Fundamental Research. – 2017. – № 3 –
URL: www.science-sd.com/471-25343 (19.09.2020).